The present invention relates to photosensitive chips for creating electrical signals from an original image, as would be found, for example, in a digital scanner, copier, facsimile machine, or other document generating or reproducing device.
Image sensor arrays typically comprise a photosensitive array of photosites which raster scan an image bearing document and convert the microscopic image areas viewed by each photosite to image signal charges. Each photosite includes one or more photodiodes, photogates or other photodetection devices. Following an integration period, the image signal charges are amplified and transferred as an analog video signal to a common output line or bus through successively actuated multiplexing transistors.
For high-performance image sensor arrays, a preferred design includes a photosensitive array of photosites of a width comparable to the width of a page being scanned, to permit one-to-one imaging generally without the use of reductive optics as taught in U.S. Pat. No. 5,473,513. In order to provide such a xe2x80x9cfull-widthxe2x80x9d array, however, relatively large silicon structures must be used to define the large number of photosites as shown in FIG. 1. A preferred technique to create such a large array is to assemble several photosensitive chips 101 through 10N end to end on a base substrate 20, each chip 10 defining a small photosensitive array thereon. The base substrate 20 is preferably a form of ceramic such as alumina, and the chips 10 are preferably made of silicon or another semiconductor material. N is defined as any whole number.
Alternatively, chip 10 may represent a charged-coupled device (CCD) or another type of photosensitive semiconductor chip.
The chips 10, which are assembled end to end to form one full-width array are created by first creating the circuitry for a plurality of individual chips 10 on a single silicon wafer. The silicon wafer is then cut, or xe2x80x9cdiced,xe2x80x9d around the circuit areas to yield discrete chips 10. Typically, the technique for dicing the chips 10 includes a combination of chemical etching and mechanical sawing. Because, on each chip 10, the photosites are spaced with high resolution from one end of a chip 10 to the other, the cutting of the chips 10 from the wafer requires precision dicing. It would be desirable to dice each individual chip 10 with a precise dimension along the photosensitive array of photosites, so that, when a series of chips 10 are assembled end-to-end to form a single page-width photosensitive array, there is a minimum disruption of spacing from an end photosite on one chip 10 to a neighboring photosite at the end of a neighboring chip 10. Typically, there is a small gap 30 between two adjacent chips 10. Ideally, the geometric centers of the photosites should be collinear and the photosites should be uniformly spaced across an entire full-width photosensitive array regardless of the configuration of silicon chips 10 forming the photosensitive array. In the prior art, all of the photosites in the chips 10 were made in a square or rectangular shape to provide a repetitive structure of photosites 40. In this way, the repetitive structure was maintained on a chip-to-chip basis, particularly in the gaps 30 between adjacent chips 10 as shown in FIG. 2.
As shown in FIG. 2, the photosites 40 typically have a rectangular shape, wherein each photosite 40 is smaller in the x-direction (fast scan direction) than the y-direction (slow scan direction or direction of document motion) to allow for electrical isolation, to limit cross talk and to allow for conductive traces to run between photosites. As a result, the optical modulation transfer function (MTF) of the system is higher in the x-direction (fast scan direction) than in the y-direction (slow scan direction). The fact that the document to be scanned moves in the y-direction further reduces the y-MTF. However, the negative consequences of the high x-MTF need to be addressed.
For example, half-tone documents typically have a certain dot frequency in the x-direction. Since a beat occurs between the dot frequency and the frequency of the photosite locations, undesirable Moirxc3xa9 patterns appear on the reproduced documents. Therefore, there is a need for a new photosensitive array of photosites, which reduces or eliminates the Moirxc3xa9 patterns particularly in the x-direction (fast scan direction).
As shown in FIG. 3, there were attempts in the prior art to improve image quality at the boundary of adjacent chips by providing photosites having two different shapes on photosensitive chips. This pattern was generally disclosed in U.S. Pat. No. 5,552,828. The regular photosites 60 have a generally square shape or slightly rectangular shape whereas the end photosites 70 have a trapezoidal shape. The advantage of the generally trapezoidal shape of end photosites 70 is that, while the overall width of each end photosite 70 is equal to that of each regular photosites 60, the geometric center of the end photosites 70 is made slightly closer to the edge of the chip 10 to help compensate for any chip spacing problems between the chips 10. However, this arrangement of hapes does not reduce or eliminate Moirxc3xa9 patterns.
U.S. Pat. No. 5,031,032 discloses a pattern of photosites for a full width photosensitive array with photosites of different colors. Although multiple geometric shapes are used to form a rectangular photosite with the three different primary colors, this arrangement of shapes does not reduce or eliminate Moirxc3xa9 patterns.
According to a first embodiment of the present invention, there is provided a photosensitive array having a fast scan direction and a slow scan direction, wherein the photosensitive array includes an array of generally rectangular photocollection areas on a chip. Each of the photocollection areas includes first and second complementary shapes, wherein the first complementary shape of one photocollection area and the first complementary shape of another photocollection area form one photosite. The second complementary shape of the one photocollection area and the second complementary shape of the other photocollection area form another photosite. Each complementary shape has a photodetection device such as a photodiode or photogate, and each complementary shape has the same surface area. In addition, the photosites are collinear. This configuration reduces the modulation transfer function in the fast scan direction thereby reducing the Moirxc3xa9 patterns. The photosensitive array may be a linear array or a two-dimensional array. Preferably, the two dimensional array has three rows of photocollection areas for the three primary colors. Further, one photosensitive array may be used to scan an image. Alternatively, a photosensitive array is mounted on a substrate adjacent to a second photosensitive array of complementary shaped photosites wherein the last shape of the photosensitive array and the first shape of the second photosensitive array are preferably complementary. The photosensitive array is preferably an array of generally rectangular buttable photocollection areas extending from one end of the chip to the other. The photosensitive arrays are preferably adapted for end to end assembly with like arrays to form a full width array. The photosensitive arrays can be mounted on a rectangular substrate to end relationship and extend from one end of the substrate to the other to form a full width photosensitive array. Examples of the complementary shapes are triangles and rounded triangles.
According to another embodiment of the present invention, there is provided a photosensitive array having a fast scan direction and a slow scan direction, wherein the photosensitive array includes an array of generally rectangular photocollection areas on a chip. Each of the photocollection areas including first, second, third and fourth complementary shapes, wherein the first and second complementary shapes of one photocollection area and the first and second complementary shapes of another photocollection area form one photosite. The third and fourth complementary shapes of the one photocollection area and the third and fourth complementary shapes of the other photocollection area form another photosite. Each complementary shape has a photodetection device such as a photodiode or photogate, and each complementary shape has the same surface area. In addition, the photosites are collinear. This configuration reduces the modulation transfer function in the fast scan direction thereby reducing the Moirxc3xa9 patterns. The photosensitive array may be a linear array or a two-dimensional array. Preferably, the two dimensional array has three rows of photocollection areas for the three primary colors. Further, one photosensitive array may be used to scan an image. Alternatively, a photosensitive array is mounted on a substrate adjacent to a second photosensitive array of complementary shaped photosites wherein the last shape of the photosensitive array and the first shape of the second photosensitive array are preferably complementary. The photosensitive array is preferably an array of generally rectangular buttable photocollection areas extending from one end of the chip to the other. The photosensitive arrays are preferably adapted for end to end assembly with like arrays to form a full width array. The photosensitive arrays can be mounted on a rectangular substrate to end relationship and extend from one end of the substrate to the other to form a full width photosensitive array. Examples of the complementary shapes are triangles and rounded triangles.
According to another embodiment of the present invention, there is provided a photosensitive array having a fast scan direction and a slow scan direction, wherein the photosensitive array includes an array of generally rectangular photocollection areas on a chip. Each of the photocollection areas includes first and second elliptical shapes, wherein the first elliptical shape of one photocollection area and the first elliptical shape of another photocollection area form one photosite. The second elliptical shape of the one photocollection area and the second elliptical shape of the other photocollection area form another photosite. Each elliptical shape has a photodetection device such as a photodiode or photogate, and each elliptical shape has the same surface area. In addition, the photosites are collinear. This configuration reduces the modulation transfer function in the fast scan direction thereby reducing the Moirxc3xa9 patterns. The photosensitive array may be a linear array or a two-dimensional array. Preferably, the two dimensional array has three rows of photocollection areas for the three primary colors. Further, one photosensitive array may be used to scan an image. Alternatively, a photosensitive array is mounted on a substrate adjacent to a second photosensitive array of complementary shaped photosites wherein the last shape of the photosensitive array and the first shape of the second photosensitive array are preferably complementary. The photosensitive array is preferably an array of generally rectangular buttable photocollection areas extending from one end of the chip to the other. The photosensitive arrays are preferably adapted for end to end assembly with like arrays to form a full width array. The photosensitive arrays can be mounted on a rectangular substrate to end relationship and extend from one end of the substrate to the other to form a full width photosensitive array. An example of an elliptical shape is a circular shape.
According to another embodiment of the present invention, there is provided a photosensitive array having a fast scan direction and a slow scan direction, wherein the photosensitive array includes an array of generally rectangular photocollection areas on a chip. Each of the photocollection areas including first, second, third and fourth elliptical shapes, wherein the first and second elliptical shapes of one photocollection area and the first and second elliptical shapes of another photocollection area form one photosite. The third and fourth elliptical shapes of the one photocollection area and the third and fourth elliptical shapes of the other photocollection area form another photosite. Each elliptical shape has a photodetection device such as a photodiode or photogate, and each elliptical shape has the same surface area. In addition, the photosites are collinear. This configuration reduces the modulation transfer function in the fast scan direction thereby reducing the Moirxc3xa9 patterns. The photosensitive array may be a linear array or a two-dimensional array. For example, the two dimensional array may have three rows of photocollection areas for the three primary colors. Further, one photosensitive array may be used to scan an image. Alternatively, a photosensitive array is mounted on a substrate adjacent to a second photosensitive array of complementary shaped photosites wherein the last shape of the photosensitive array and the first shape of the second photosensitive array are preferably complementary. The photosensitive array is preferably an array of generally rectangular buttable photocollection areas extending from one end of the chip to the other. The photosensitive arrays are preferably adapted for end to end assembly with like arrays to form a full width array. The photosensitive arrays can be mounted on a rectangular substrate to end relationship and extend from one end of the substrate to the other to form a full width photosensitive array. An example of an elliptical shape is a circular shape.
The chips of the embodiments of the present invention can be used for single chip applications or assembled to form full width arrays. The chips can be incorporated into a digital copier including a raster scanner scanning documents to generate digital image signals; a controller directing a raster output scanner to expose a photoconductive belt to create an electrostatic latent image based on image signals received from the raster input scanner; a developer applying toner to the latent image; a transfer station transferring the toner of the latent image to a sheet of paper; and a fuser permanently affixing the toner to the sheet of paper. A raster input scanner includes a plurality of generally rectangular chips, which are mounted on a substrate forming an array of generally rectangular buttable photocollection areas. Each complementary shape has a photodetection device, each complementary shape has the same surface area, and the photosites are collinear. Each of the photocollection areas can include first and second complementary shapes, wherein the first complementary shape of one photocollection area and the first complementary shape of another photocollection area form one photosite. The second complementary shape of the one photocollection area and the second complementary shape of the other photocollection area form the second photosite. Alternatively, each of the photocollection areas can include first, second, third and fourth complementary shapes, wherein the first and second complementary shapes of one photocollection area and the first and second complementary shapes of another photocollection area form one photosite. The third and fourth complementary shapes of the one photocollection area and the third and fourth complementary shapes of the other photocollection area form another photosite. Examples of the complementary shapes are triangles, rounded triangles, ellipses and circles.